Effectiveness of isopropyl myristate/cyclomethicone D5 solution of removing cuticular hydrocarbons from human head lice (Pediculus humanus capitis).

Barnett et a I. BMC Dermatology 201 2, 1 2:1 5
http://www.biomedcentral.eom/1 471-5945/1 2/1 5

Dermatology

RESEARCH ARTICLE Open Access

Effectiveness of isopropyl myristate/
cyclomethicone D5 solution of removing cuticular
hydrocarbons from human head lice {Pediculus
humanus capitis)

Eric Barnett 1 " Kathleen G Palma 1 , Bert Clayton 1 and Timothy Ballard 2

Abstract

Background: In the treatment of human head lice infestation, healthcare providers are increasingly concerned
about lice becoming resistant to existing pesticide treatments. Traditional pesticides, used to control these pests,
have a neurological mechanism of action. This publication describes a topical solution with a non-traditional
mechanism of action, based on physical disruption of the wax layer that covers the cuticle of the louse exoskeleton.
This topical solution has been shown clinically to cure 82% of patients with only a 10-minute treatment time,
repeated once after 7 days. All insects, including human head lice, have a wax-covered exoskeleton. This wax,
composed of hydrocarbons, provides the insect with protection against water loss and is therefore critical to its
survival. When the protective wax is disrupted, water loss becomes uncontrollable and irreversible, leading to
dehydration and death. A specific pattern of hydrocarbons has been found in all of the head louse cuticular wax
studied. Iso-octane effectively removes these hydrocarbons from human head lice's cuticular wax.

Methods: A method of head louse cuticle wax extraction and analysis by gas chromatography was developed.
Human head lice {Pediculus humanus capitis) were collected from infested patients and subjected to any of three
extraction solvents comprising either the test product or one of two solvents introduced as controls. A gas
chromatograph equipped with a flame ionization detector (GC/FID) was used to determine the presence of
hydrocarbons in the three head lice extracts.

Results: In the study reported herein, the test product isopropyl myristate/cyclomethicone D5 (IPM/D5) was shown
to perform comparably with iso-octane, effectively extracting the target hydrocarbons from the cuticular wax that
coats the human head louse exoskeleton.

Conclusions: Disruption of the integrity of the insect cuticle by removal of specific hydrocarbons found in the
cuticular wax appears to offer a mechanism for killing lice without the likelihood of encountering genetic
resistance.

Keywords: Non-pesticidal, Head lice, Therapy, Treatment, Resistance, Permethrin, Pyrethroid, Isopropyl myristate,
Cyclomethicone D5, Decamethylcyclopentasiloxane

* Correspondence: ebarnett@piedmontpharma.com

1 Piedmont Pharmaceuticals, Greensboro, NC, USA

Full list of author information is available at the end of the article

O© 2012 Barnett et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
BiolVlGCl Central Commons Attribution License (http://creativecommons.Org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.

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Background

Head lice a global issue

Head lice infestation is a fairly common problem glo-
bally, with 6-12 million cases in children ages 3-11
reported annually in the US alone [1], and is typically
observed in the school-aged population. Infestation is
transmitted most commonly by physical head-to-head
contact, but also by sharing hats, hairbrushes, head-
bands, or clothing.

Insect exoskeleton-based cuticular hydrocarbons are
universal

Head lice, like all insects, have a protective waxy cover-
ing on the epicuticle (outer layer of the cuticle on their
exoskeletons) that acts as waterproofing for the insect.
Therefore, without the wax, the insect is vulnerable to
uncontrollable dehydration, and death. These cuticular
lipids are composed of various hydrocarbons whose pat-
terns vary by insect [2].

A challenge to cure

Head lice infestations can be difficult to cure completely,
and typically require multiple treatments. Some products
may act by suffocation of the insects; these may require
up to an 8 hour application time. However with add-
itional changes made to the suffocant formulation the
8 hour treatment can be decreased substantially. Eggs
(nits) are attached to the hair with protein 'glue' which
makes the eggs difficult to remove. Even after treatment,
viable eggs may hatch and young nymphs emerge. Iso-
propyl myristate (IPM) and cyclomethicone D5 do not
have an effect on egg development. Only after the oper-
culum (the opening the nymphal louse emerges from)
begins to open (4-5 days) can the IPM and cyclomethi-
cone D5 come in contact with the nymph inside. Once
the nymph is exposed to the formulation, the nymph
will die whether it has emerged from the egg or not.

Pesticide therapies

Some medical practitioners recommend pesticide treat-
ments containing permethrin, pyrethrin, or malathion.
These therapies have been the first line of treatment for
head lice since World War II. Today more interest is
being placed on treatments that are alternatives to con-
ventional pesticides with different modes of action.
These new therapies are unlikely to allow development
of resistance in the head louse population.

Increasing resistance to pesticides

Of particular concern, is the growing body of evidence
suggesting a global emergence in head lice of significant
resistance to pesticide products containing permethrins
and pyrethroids. Marcoux et al. reported that the wide-
spread use of pyrethrins and pyrethroids have led to

significant resistance across various countries including
Canada, Argentina, Australia, the United Kingdom, the
United States, Japan, Korea, and Israel. This resistance
results in prolonged infestations, reinfestation and safety
concerns resulting from overdosing with a treatment
therapy. Resistance factors associated with insensitivity
to DDT, pyrethrins and pyrethroids were found by Mar-
coux to be present in 97% of head lice collected from
several Canadian cities [3].

Chemistry of Isopropyl Myristate/Cyclomethicone D5
(IPM/D5)

Isopropyl myristate/cyclomethicone D5, is a topical for-
mulation containing 50/50 w/w Isopropyl myristate/dec-
amethylcyclopentasiloxane. Isopropyl myristate, with the
chemical formula CH 3 (CH 2 ) 12 COOCH (CH 3 ) 2 [4], is an
ester of myristic acid, an essential fatty acid derived from
palm kernel oil and isopropyl alcohol. IPM is used to
dissolve lanolin and other oils, and is commonly used as
a degreasant or softener in sunscreens, face creams and
lipsticks. Due to its probable physical mechanism of ac-
tion (dissolution of the waxy cuticular covering found
on the louse exoskeleton), head louse resistance is not
expected to develop against isopropyl myristate [3]. Dec-
amethylcyclopentasiloxane (cyclomethicone D5), with
the chemical formula cyclo- (Me 2 SiO) 5 [5] is a spreading
agent commonly used in cosmetics, that helps the iso-
propyl myristate to thoroughly coat the hair. Some adul-
ticide activity has been noted in laboratory studies at
concentrations higher than 50%. Cyclomethicone D5,
which is used extensively as an excipient, can be found
in some head lice treatments in concentrations as high
as 96%.

About this study

This study was conducted in an attempt to investigate
the mechanism by which IPM/D5 is able to kill head lice
after 10 minutes contact. It is well understood that in-
sect dehydration can kill quickly, and it was expected
that IPM/D5 was acting via a physical mechanism to dis-
rupt the protective waxy coating on the louse exoskel-
eton. This study investigates this possible mechanism of
action by specifically determining the removal efficiency
of head louse cuticular hydrocarbons using a 50/50 w/w
mixture of isopropyl myristate/cyclomethicone D5.

Methods

A method of head louse cuticle wax extraction and ana-
lysis by gas chromatography was initially developed by
CW Scherer [2]. This methodology was scaled up 10-
fold, using 10 lice per sample (instead of 1 louse) and 80
uL extraction solvent instead of 8 uL. Work was con-
ducted at En-Cas Analytical Laboratories of Winston-
Salem, North Carolina, USA.

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Materials

Human head lice (Pediculus humanus capitis) used in
this work were received as untreated live head lice col-
lected from infested patients and shipped the day of col-
lection at room temperature conditions. Head lice were
stored refrigerated for several hours prior to testing.
Three different extraction solvents were used:

• 50/50 w/w isopropyl myristate/
decamethylcyclopentasiloxane (cyclomethicone D5)
- (IPM/D5)-subject product

• Iso-octane - a laboratory determined optimal
extraction solvent for hydrocarbons

• 50/50 methanol/water - control

Sample preparation

Ten head lice (per sample) were transferred individually
with tweezers to clean empty 350- uL glass GC vial
inserts. Specimens were covered with 80 uL of any of
the three extraction solvents then allowed to incubate at
room temperature for 10 minutes. The samples were
then mixed by aspiration. Solvent samples containing
the extracted lice cuticle hydrocarbons (CHCs) were
transferred to a new unused insert contained in a 2-mL
crimp top vial which was subsequently sealed and held
for later analysis.

Gas chromatography

A gas chromatograph equipped with a flame ionization
detector (GC/FID) was used to determine the presence
of hydrocarbons in the three head lice extracts. A

standard containing a series of known hydrocarbons
(C21-40) was used for qualitative sample comparison.

Results

In his dissertation, Scherer reported four specific hydro-
carbons present in significant amounts in every head
louse sample he studied [2]. These four hydrocarbons
represent approximately 50% of the cuticle hydrocarbons
of head lice, and had retention time indices (RI) of 2500,
2700, 2900 and 3075.

The peaks that corresponded to the four retention
time indices attributed to the head louse by Scherer
were integrated and compared qualitatively to the alkane
standard.

The alkane calibration mixture, when run by GC, pro-
duced a chromatogram with regular peaks correlating
with each respective component. The retention time in-
dices for the four specific hydrocarbons of interest were
2500, 2700, 2900 and 3075.

The baseline experiment, comparing the chromato-
gram of the scaled-up iso-octane extraction (10 lice in
80 uL iso-octane) correlated very well with the analo-
gous chromatogram published by Scherer. As expected,
the main peaks observed for this sample had retention
time indices of 2500, 2700, 2900 and 3075.

In a control experiment, 10 head lice were co-
extracted by immersion with 50/50 methanol: water.
This 50/50 methanol: water solution was found visually
to provide entire wetting of the head louse. However, the
chromatogram produced from the analysis of the aque-
ous methanol extract showed a complete lack of CHC
removal efficiency.

Figure 1 Gas Chromatogram demonstrating head lice epicuticle hydrocarbon extraction efficiency of isopropyl myristate/
cyclomethicone D5 vs. iso-octane (offset for visualization purposes).

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As seen in the gas chromatogram overlay (Figure 1),
Isopropyl myristate/cyclomethicone D5 (IPM/D5) had
equivalent efficacy extracting the four target hydrocar-
bons from the lice cuticular wax as iso-octane. The IPM/
D5 (isopropyl myristate/cyclomethicone D5) (red) chro-
matogram is artificially shifted to the right, offset for
visualization purposes, because the four peaks of inter-
est were virtually identical in peak shape and height to
those in the iso-octane chromatogram.

Discussion

The study reported here was conducted to investigate
the mechanism of action of IPM/D5, focusing on the po-
tential role of IPM/D5 in physically disrupting the integ-
rity of the head louse body's outermost protection
against dehydration. The cuticular wax that covers the
exoskeleton of insects is vital in protecting them against
dehydration and death. The wax layer of the epicuticle
(outer layer) is composed of a matrix of hydrocarbons,
and four specific hydrocarbons identified to be consist-
ent among head lice by Scherer were selected for study
in this work.

Isopropyl myristate/decamethylcyclopentasiloxane
(IPM/D5) is a colorless, odorless solution. It was theo-
rized that the mechanism of action for this solution
involved disruption of the protective waxy coating cov-
ering the louse exoskeleton, leading to uncontrollable
dehydration, and death.

It is known that suffocation of head lice is a slow
process and can take up to 8 hours or more. Isopropyl
myristate/cyclomethicone D5 has been shown clinically
to have an 82% cure rate after two 10-minute treatments
(one week apart) and therefore, suffocation is not a likely
mechanism of action.

In this study gas chromatography was used to compare
the hydrocarbon extraction efficiency of isopropyl myris-
tate/cyclomethicone D5 with that of iso-octane as a con-
trol reference. Hydrocarbons specific to the waxy layer
of the epicuticle of head lice were evaluated. This study
showed that isopropyl myristate/cyclomethicone D5 ef-
fectively extracted the target hydrocarbons. Therefore,
we deduce that the fast acting mechanism of action seen
with IPM/D5 is via epicuticular hydrocarbon extraction,
resulting in disruption of the waxy layer of the cuticle,
followed by rapid water loss and death by dehydration.

Overcoming resistance

These data support why a treatment with a physical
mode of action, such as isopropyl myristate/cyclomethi-
cone D5, can be comparable to a traditional pesticide.
Pesticides, however, as evidenced in recent clinical trials,
are increasingly facing issues of resistance globally. Bur-
gess reported from a UK clinical study investigating
IPM/D5 vs. 1% permethrin that IPM/D5 had 82% cure

rate whereas the permethrin had only a 19% cure rate
[6]. The development of resistance to pesticides such as
permethrin is well documented [3] .

Conclusions

Isopropyl myristate/cyclomethicone D5 (IPM/D5) ex-
tracted the same specific cuticular wax hydrocarbons as
those identified by Scherer to be critical to the survival
of the head louse, therefore it can be deduced that IPM/
D5 acts by a physical mode of action to kill head lice via
disruption of the protective wax coating resulting in
rapid dehydration. These data, combined with clinical
study data support an explanation of the mechanism of
action by dehydration, not suffocation.

Isopropyl myristate/cyclomethicone D5 is a colorless,
odorless formulation that kills human head lice within
10 minutes by employing a physical mechanism of ac-
tion that would not likely be subject to resistance. This
formulation could be considered as a viable alternative
to conventional pesticides.

Abbreviations

DDT: Dichlorodiphenyltrichloroethane; FDA: Food and Drug Administration;
GC: Gas Chromatograph; GC/FID: Gas Chromatograph equipped with a
Flame Ionization Detector; IPM/D5: Isopropyl Myristate/cyclomethicone D5;
MHRA: Medicines and Healthcare products Regulatory Agency; Rl: Retention
Index; w/w: By Weight (to describe concentration in solution)

Competing interests

Piedmont Pharmaceuticals sponsored the study. Eric Barnett (EB) and
Bert Clayton (BC) are employees of Piedmont Pharmaceuticals, the
company that developed the non-pesticidal human head lice treatment
composed of Isopropyl myristate/cyclomethicone D5 discussed in this
paper. Kathleen Palma (KP) is a paid consultant of Piedmont
Pharmaceuticals. This solution is marketed as Full Marks™ Solution by
Reckitt Benckiser in certain European countries, Australia and Russia; as
Resultz® by Medical Futures in Canada, Takeda in Belgium, and Lapidot
in Israel. Tim Ballard (TB) of En-Cas Analytical Laboratories was paid on a
fee for service basis to conduct the laboratory work, and does not have
a competing interest.

Authors' contributions

KP designed the study and gave final approval to the publication. EB
managed the overall research project and edited the publication. BC
supervised the technical analysis. TB carried out the technical analysis. All
authors read and approved the final manuscript.

Authors' information

Kathleen Palma is a PhD entomologist with over 20 years of experience in
developing parasitology medicines for the pharmaceutical industry. Dr Palma
is a co-inventor of the subject product.

Acknowledgements

We would like to acknowledge Kathy Meserve, President of Sequoia
Research, Inc. of North Carolina, who provided medical writing services on
behalf of Piedmont Pharmaceuticals, LLC.

We would also like to acknowledge CW Scherer, whose analytical
method developed at the University of Florida was used to
demonstrate the mechanism of action of the head lice treatment
discussed in our paper.

Author details

1 Piedmont Pharmaceuticals, Greensboro, NC, USA. 2 En-Cas Analytical
Laboratories, Winston-Salem, NC, USA.

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Received: 25 January 2012 Accepted: 29 August 2012
Published: 3 September 2012

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3. Marcoux D, Palma KG, Kaul N, Hodgdon H, Van Geest A, Previte DJ, Abou-
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5. Wikipedia: Decamethylcyclopentasiloxane. http://en.wikipedia.org/wiki/File:
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doi:1 0.1 1 86/1 471-5945-1 2-1 5

Cite this article as: Barnett et al.\ Effectiveness of isopropyl myristate/
cyclomethicone D5 solution of removing cuticular hydrocarbons from
human head lice {Pediculus humanus capitis). BMC Dermatology 2012
12:15.

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